SGR J1935+2154 is a Galactic magnetar, a non-accreting neutron star powered mainly by magnetic energy dissipation (see [1]}, [2]}, [3]} for recent reviews). This class of high energy sources is characterized by strong variability and recurrent bursts of hard X-rays/soft gamma-rays (hence the name soft gamma-ray repeaters, SGRs), that have typical duration \(\lesssim \)  1 s and peak luminosity \(\lesssim 10^{39-41}\)  erg s\(^{-1}\) . Hyper-energetic bursts with peak luminosity reaching \(10^{47}\)  erg s\(^{-1}\) , known as giant flares, have also been emitted sporadically by a handful of magnetars (e.g. [4]}).
